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Editorial Team
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Asked: 2026-05-25T14:47:28+00:00

In class I’ve been tasked with writing a C program that decompresses a text

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In class I’ve been tasked with writing a C program that decompresses a text file and prints out the characters it contains. Each character in the file is represented by 2 bits (4 possible characters).

I’ve recently been informed that a byte is not necessarily 8 bits on all systems, and a char is not necessarily 1 byte. This then makes me wonder how on earth I’m supposed to know how many bits got loaded from a file when I loaded 1 byte. Also how am I supposed to keep the loaded data in memory when there are no data types that can guarantee a set amount of bits.

How do I work with bit data in C?

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1 Answer

  1. Editorial Team

    This then makes me wonder how on earth I’m supposed to know how many
    bits got loaded from a file when I loaded 1 byte.

    You’ll be hard pressed to find a platform where a byte is not 8 bits. (though as noted above CHAR_BIT can be used to verify that). Also clarify the portability requirements with your instructor or state your assumptions.

    Usually bits are extracted using shifts and bitwise operations, e.g. (x & 3) are the rightmost 2 bits of x. ((x>>2) & 3) are the next two bits. Pick the right data type for the platforms you are targettiing or as others say use something like uint8_t if available for your compiler.

    Also see:
    Type to use to represent a byte in ANSI (C89/90) C?

    I would recommend not using bit fields. Also see here:

    When is it worthwhile to use bit fields?

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